Etiological surveillance of bacillary dysentery in Nanjing, Jiangsu, 2007-2011

Objective To understand the serotype, drug resistance, carriage of virulence genes and PFGE patterns of Shigella in Nanjing from 2007 to 2011and provide evidence for the prevention and control of bacillary dysentery. Methods Totally 75 Shigella strains were isolated from hospitals in Nanjing to conduct serotyping, drug resistance test, virulence gene detection and PFGE. Results Of the 75 Shigella strains, 54 (72.0%) were identified as S. sonnei and 21 (28.0%) as S. flexneri. Shigella sonnei was predominant during this period except 2010, when S. flexneri serotype X was predominant, and All the strains isolated were resistant to ampicillin, achromycin and sulfamethylisoxazole and the resistance rate ranged from 61.1% to 95.2%. Up to 88.0% of the resistant strains were multiple drug resistant. The carriage rates of virulence genes ipaH, sen, set1 and ial were 100%, 46.7%, 24.0% and 48.0%, respectively. Virulence gene type Ⅰ was predominant in S. flexneri strains (66.7%), and type Ⅶ (61.1%) and Ⅳ (25.9%) in S. sonnei strains. All the S. sonnei strains had 20 PFGE patterns, the patterns S7, S8 and S10 (53.7%) were predominant, which shared similarity of above 95%. All the S. flexneri strains had 17 PFGE patterns. Conclusion The serotype of Shigella changed constantly in Nanjing, there is a trend of S. flexneri to be predominant circulating strain instead of S. sonnei. The multidrug resistance of Shigella strains is very serious. Virulence gene type I was predominant in S. flexneri strains and type Ⅶ and Ⅳ in S. sonnei strains.